Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND O~ THE INVF.NTION
Field of the Invention
This invention relates to a video tape recorder
having rotary magnetic heads, and particularly to the type of
recorder known as a time lapse video tape recorder that may
be energized by a continuous series of video signals but is
controlled to record, normally, only selected, time-spaced
video signals. The invention is especially directed to a
system that provides for playback of the recorded signals,
usually in the next equal time interval after such recording
takes place, to determine whether or not the recording
apparatus is operating properly.
The Prior Art
The purpose of a time lapse video tape recorder
(hereinafter referred to as a time lapse VTR~ is to record
only the relatively small number of signals corresponding to
video images, even though such signals are applied to the
apparatus on a continuous basis. Time lapse VTRs are
especially useful for surveillance of banks, department stores,
and other places in which a high percentage of the television
images that might be recorded is of no use. In order to
eliminate unnecessary use of video tape in such VTRs, the
continuous video signal is gated so that only an occasional
frame or field interval is recorded. The tape can be run at
a lower speed corresponding to the intermittency of the signal
to be recorded. For example, if only 1/60 of the fields are to
be recorded, the tape may be run at 1/60 of the normal speed,
without causing the tracks on which the signals are recorded
to overlap each other so as to obliterate the recorded signals.
However, in such apparatus the rotary magnetic head usually
runs at the same speed as in a normal tape recorder and thus
each incremental area of the tape is subjected to a high rate
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of wear due to the repetitive, frictional, scanning of the
tape by the transducers. As a result, the magnetic coating
material is likely to wear off, thereby making it impossible
to produce a proper recording, and the air gaps in the magnetic
transducers are likely to be blocked, thereby further inter-
fering with the ability of the apparatus to record images
properly or, indeed, to record them at all. Furthermore,
such apparatus is likely to be operated continuously for a
long period of time, for example 24 hours or even much longer,
without being checked to see that the images are satisfactory.
In any of those cases, when the rare occasion makes it absolutely
essential to produce a properly recorded image, the apparatus
may be unable to do so.
SUMWARY OF THE INVENTION
It is one of the objects of the present invention to
provide a time lapse VTR in which the recorded information
is monitored by being played back on a regular basis, usually
immediately after each recording.
A further object of the invention is to provide
automatic means for checking at least certain essential qualities
of the reproduced signal so as to actuate an alarm if the
reproduced signal is defective.
In a time lapse VTR according to the present
invention, certain intervals of a continuously available signal
are allowed to pass through a gate and to energize magnetic
transducer means so as to be recorded on a magnetic recording
medium. Typically the recorded interval will be a television
field or frame. The apparatus is further provided with
switching means controlled in a manner synchronous with the
gate circuit to utilize the transducer means to play back the
recorded signal, preferably in the next field or frame interval.
If the apparatus includes two magnetic transducers
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spaced 180 apart in a rotary magentic head, one of the
transducers may be used to record selected field intervals
and the other to play back the same intervals. Since the
tape moves relatively slowly, the second transducer traces
out substantially the same track that was recorded by the
first transducer. If the two fields making complete frame
are to be recorded, it may be preferable, due to the slow
linear movement of the tape, to offset the two diametrically
opposite transducers so that they will not trace out the
same tracks but will trace out adjacent tracks. Even in
such circumstances, the slow movement of the film means
that there will be sufficient overlap of the traced out tracks
so that if the transducers are switched from the recording
condition to the playback condition immediately after the
recording interval has been completed, the played back signal
will still give sufficient indication of the quality of the
recording, particularly if that indication of quality is
primarily based on the amplitude of the recording.
In another embodiment of the invention an ordinary
video tape recorder can be used in which the tape ~oves at
normal speed but the only signals that are recorded are those
that correspond to a small fraction of the continuously
available television image signals. Since only occasional
images are recorded, it is not necessary that the tape be
moved continuously. Instead, it can also be moved inter-
mittently, being brought up to speed just in time to receive
the signal to be recorded, and then being stopped as soon
as possible after the recording and evaluation playback has
taken place.
More particularly, there is provided a time lapse
video tape recorder comprising:
A. magnetic transducer means moving at a predetermined
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speed;
B. means for selecting certain video image signals
of a succession of said signals and for recording only said
certain signals on said medium during intermittent recording
intervals;
C. means for moving a recording medium past said
transducer means at an average rate of speed too low to record
all of said video image signals on said medium; and
D. means to monitor the recorded signals during
0 intervals succeeding the intermittent recording intervals.
BRIEF DESCRIPTION OF THE DRA~INGS
Fig. l is a block diagram of time lapse video magnetic
recording apparatus according to the present invention.
Fig. 2 is a graphical representation of signals that
occur in the operation of the apparatus in Fig. l.
DETAILED DESCRIPTION OF TIIE INVENTION
In the apparatus in Fig. 1 video magnetic recording
tape l is scanned by a pair of magnetic transducers 2 located
at opposite ends of an arm 3 attached to a rotary shaft ~
driven by a motor 5 at a predetermined speed. Typically, the
arm 3 is rotated at a speed of 30 cycles per second, or 1800rpm.
The magnetic tape is guided in a helical path around the rotary
head in the usual manner and is pulled along by a capstan 6
and pinch roller 7. The capstan is driven by a motor 8, the
rotational speed of which is detected by a detector 9 and used
to generate a signal applied to a control circuit 10 that
controls the exact speed of the motor 8.
Television signals are generated in a television
camera 11 to which horizontal synchronizing signals HD and
vertical synchronizing signals VD are applied from a synchron-
izing signal generator 12. The video signal produced in the
camera 11 is connected to a frequency modulator 13 to modulate
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the frequency of a carrier therein.
The vertical synchronizing signals from the
generator 12 are also connected to a frequency divider 14 that
divides them by 2 to produce an output signal, normally a
pulse signal, that has a repetition rate of 30 cycles per
second. A pulse generator 15 includes a magnet attached to
the rotating shaft 4 and a pickup head that derives electric
pulses due to the field of the rotating magnet on the shaft.
These pulses occur, under synchronous conditions, at the
rate of 30 per second and are applied to a phase comparator
16 to be compared with the 30 cycle signal from the frequency
divider 14. The output of the phase comparator 16 is connected
back to the motor 5 so that both its rotational speed and its
phase position are controlled.
The vertical synchronizing signals from the sync
generator 12 are also applied to a counter 17 that may be set
to count any desired number. For example the counter 17 may be
set to produce one output pulse for each 60 input pulses so
that the output signal has a repetition rate of one cycle
per second. The output of the counter 17 is connected to a
recording amplifier 18 which, in turn, is connected to a
stationary recording head 19 that records control pulses along
one edge of the tape. The location of each of the latter
pulses has a certain relationship to the location of each track
on the tape on which one of the transducers 2 has recorded a
signal. The output of the counter 17 is also connected to the
control circuit 10 to be compared with the signal from the
rotation detector 9 to control the rotational speed of the
motor 8.
The frequency modulated video signal from the
frequency modulator 13 is connected to a gate circuit 20. The
output of the gate circuit 20 is connected through a recording
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amplifier 21 to one of the terminals 22b of switching means
22 here illustrated as a relay having a movable arm 22a and
two fixed terminals 22b and 22c. The arm 22a is connected to
the transducers 2 to supply the signal to be recorded on the
tape 1.
The terminal 22c is connected to a playback amplifier
23 which, in turn, supplies an output signal to a level
detector 24. The level detector detects the amplitude of the
output signal of the playback amplifier 23 and supplies a
signal to an alarm 25 that may be an audible or visual alarm
or both. The alarm 25 may also actuate means to disable the
apparatus to prevent any further attempt to use it until it
is returned to proper operating conditions.
The output of the counter 17 is connected to the SET
terminal of the flip-flop 26, and the output of the flip-flop
26 is connected through a diode 27 to the SET terminal of
a second flip-flop 28. The video synchronizing signal VD from
the sync generator 12 is connected to the RESET terminals
of both of the flip-flops 26 and 28. The output of the flip-
flop 26 is also applied to a gating signal input terminal ofthe gate circuit 20. The output of the flip-flop 28 is
applied to the switching means 22 to control the operation of
the movable arm 22a.
The operation of the apparatus in Fig. 1 will be
described with reference to the signals graphically illustrated
in Fig. 2. The vertical synchronizing signals VD are
illustrated in the top line of signals in Fig. 2 as positive
pulses that have a fixed repetition rate. The counter 17 counts
a selected number of vertical synchronizing pulses VD, for
example 60 pulses, and produces an output signal Sl that may
be, for example, a positive pulse at the time to. The signal
Sl sets the flip-flop 26 to initiate a gating signal S2 to be
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applied to the gate circuit 20. The end of the gate signal S2
occurs when the flip-flop 26 is reset. In the illustrated
embodiment, this occurs at the next succeeding vertical sync
pulse VD so that the gate signal lasts from the time to to the
time tl.
The flip-flop 28 is set by the trailing edge of the
signal S2 and it also lasts until the flip-flop 28 is reset.
As in the case of the flip-flop 26, the flip-flop 28 is reset
by the next vertical sync pulse at the time t2. Thereafter,
the flip-flops 26 and 28 remain reset until the counter 17
produces another pulse Sl at the time tlo. If the counter
17 counts down by 60:1, the pulses Sl recur at the rate of
once each second. The second pulse Sl at the time t'o in-
itiates another se~uence, including the pulse S2 between the
times t'o and t'1 and the pulse S3 between the times t'l and t'2.
The switching means 22 has a normal condition in
which the movable arm 22a connects with the terminal 22b to
receive signals from the recording amplifier 21 each time
such signals are allowed to pass through the gate circuit 20.
The ~ignal S3 applied to the switching means 22 causes the
movable arm 22a to switch over and engage the terminal 22c.
This takes place during the vertical field interval and
immediately following the interval in which the last video
image signal was recorded on the tape 1. As a result, the
transducer 2 diametrically opposite the one that recorded the
last signal will play back that recording. Since the tape
is moving very slowly, the areas traced out by the two
diametrically opposite transducers 2 overlap to a great extent.
The signal picked up by the second transducer 2 is then fed
back through the movable arm 22a and the fixed terminal 22c
to the playback amplifier 23. The level of the output signal
of the playback amplifier 23 is detected and, if it is not
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sufficient, results in actuating the alarm 25. Although the
duration of each of the pulses in the signals S2 and S3 in Fig.
2 indicates that the recording, and therefore, the playback
- takes only 1/60 of a second and thus allows the presentation
of only one field rather than the interlaced two fields that
make up a complete frame, the duration of each of the pulses
in the signals S2 and S3 may be made twice as great so as to
permit recording and then playback of a complete frame at the
selected, spaced intervals. The spacing may be one frame
per second or any other desired figure.
Arrangements may be made to speed up the movement
of the tape 1 at any time it is desired to record a greater
percentage of the available video image signals. For example,
in the case of apparatus being used to monitor a bank,
actuation of a silent alarm may be used to cause the video
apparatus to record each successive field. This would
require changing the count of the counter 17, and if each
field were being recorded, it would require deactivation of
the switching means 22, since there would be no time available
to monitor the recorded signals.
Alternatively, the tape 1 might be moved at the
usual video tape recording speed but with only occasional
fields or frames being recorded. In that case the monitoring
transducer of the pair of transducers 2, or a monitoring
pair of transducers, would preferably be offset to trace out
the same track areas on which signals had been recorded in
order to monitor the operation by the apparatus in the manner
contemplated in this invention. One advantage of moving the
tape 1 rapidly at all times would be that it would be easy
to record each field without having to speed up the movement
of the tape. ~owever, an alternative slowing down of the tape
1 during quiet times might be desirable rather than to have
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most of the tape pass through the apparatus without having any
recording made on it. In that case the motor 9 could be
operated intermittently and should be timed to bring the tape
1 up to proper operating speed just before the beginning of
each interval S2 and keep it at that speed until just after
each interval S3.
It will be understood that various modifications
could be made in the apparatus without departing from the
true scope of the present invention as defined by the following
claims.
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